The invention relates to a motor vehicle comprising improved means for managing gear shifts in a fully automatic transmission.
The invention relates more particularly to a motor vehicle comprising a fully automatic transmission, of the type comprising a transmission control unit and an engine management unit, of the type in which the management unit receives, from a throttle pedal, information representative of the torque demand from the driver, on the basis of which information it is capable of controlling the operation of the engine, of the type in which the engine is capable of supplying information to the transmission control unit, and of the type in which the engine management can be modified as a function of information transmitted by the transmission control unit to the engine management unit.
In vehicles equipped with purely mechanical transmissions, in which the transmission, with stepped ratios, is connected to the engine via a friction clutch and in which the driver himself selects and engages the ratios via a gearshift lever, it is the driver who has to manage the gearshifting as best he can in order that these gearshifts occur entirely smoothly.
In order to do that, he controls, on the one hand, the engine speed, using the throttle pedal and, on the other hand, the progressive disengagement and engagement of the clutch, by his action on the clutch pedal.
Automatic transmissions have been in existence for many years now. This category includes, in particular, conventional automatic transmissions in which various planetary gear sets define predetermined stepped ratios, the ratios being selected by actuating various brakes or clutches which selectively immobilize certain components of the planetary gear set(s) so as to determine a gear ratio between the output shaft and the input shaft of the transmission.
Another type of automatic transmission consists of conventional mechanical transmissions with positive-engagement mechanisms, in which transmissions the ratios are selected and engaged not directly by the driver by means of a lever, but now using actuators managed by a control unit. It is possible for these actuators to operate only at the express behest of the driver, in which case the latter retains full control over the timing of the gearshift, or, on the other hand, it is possible for gearshifting to take place automatically, under the control of the control unit, as to a function of parameters similar to those used for determining the gearshift moments in a conventional automatic transmission.
A transmission such as this will be known in the following part of the text as a semiautomatic transmission.
Incidentally, it will be seen that certain aspects of the invention can equally be applied to transmissions with no stepped ratios, such as belt-driven continuously variable transmissions.
Particularly in the case of fully automatic transmissions, it has become apparent that very good control over the gearshift phase is of overriding importance for good vehicle drivability and passenger comfort. Such drivability and comfort can be obtained only by completely eliminating any lack of smoothness likely to occur during gearshifts. Now, particularly in conventional automatic transmissions and in semiautomatic transmissions it is necessary, during gearshifts, to couple and uncouple friction members by means of which the motive power of the engine is transmitted to the wheels of the vehicle. The disengagement and engagement of these friction couplings assume transient phases which are difficult to control perfectly because these are phases in which two elements are slipping one with respect to the other.
These problems are exacerbated particularly when it is not the driver who decides the timing of the gearshift because, in such an instance, he generally keeps the throttle pedal depressed which means that the gearshift may occur while the engine is delivering a relatively high torque.
In order to overcome this drawback, it is already known practice to contrive for the engine to be managed during the gearshift in such a way that it supplies just part of the torque demanded by the driver, for example by reducing this demand by a fixed percentage.
This solution does not, however, make it possible to obtain results which are entirely satisfactory in all cases, particularly where, during the gearshift, the torque demand expressed by the driver varies wildly.
It is therefore an object of the present invention to provide a new motor vehicle architecture in which, to culminate in the smoothest possible gearshifts, the requirements associated with the transmission can take precedence over those imposed by the
To this end, the invention proposes a motor vehicle of the type described previously, characterized in that, for certain phases of operation of the vehicle, the transmission control unit inhibits the action of the torque demand information, for which it substitutes an engine management command to which the management unit is subordinated.
According to other features of the invention:
when shifting from an old gear ratio to a new gear ratio which is lower, the transmission control unit transmits to the engine management unit, a management command whereby the engine is managed to cause it to follow a given speed variation curve;
the transmission ratios are determined by whether friction couplings are disengaged or engaged, the transmission is connected to the engine by a hydraulic torque converter, and when shifting from an old gear ratio to a new gear ratio which is lower, the transmission control unit transmits to the engine management unit a management command whereby the engine is managed such that an input shaft of the transmission follows a given speed variation curve;
the transmission ratios are determined by whether friction couplings are disengaged or engaged, the transmission is connected to the engine by a hydraulic torque converter, when shifting from an old gear ratio to a new gear ratio which is higher, the transmission control unit transmits to the engine management unit, during a step in which it is detected that the new ratio has bitten, a management command whereby the engine is managed so that it provides a bite detection torque;
bite is detected when the onset of the drop in the rotational speed of an input shaft of the transmission is measured;
the bite detection torque is a constant torque;
when shifting from an old gear ratio to a new gear ratio which is higher, the transmission control unit transmits to the engine management unit, during an engine speed decrease step, a management command whereby the engine is managed so that it supplies an engine speed decrease torque;
the engine speed decrease torque is determined by the control unit so that the duration of the engine speed decrease step is more or less equal to a predetermined duration;
the engine speed decrease step begins when the biting of the new ratio is detected;
the value of the engine speed decrease torque is a value that is constant during the engine speed decrease step;
the value of the engine speed decrease torque is a value which changes during the engine speed decrease step as a function of the torque demanded by the driver;
the value of the engine speed decrease torque is a value which depends on the level of torque demanded by the driver;
the transmission control unit receives the torque demand information supplied by the throttle pedal, the torque demand information is compared by the control unit with a maximum torque value, and when the torque demand remains higher than the maximum torque value for a predetermined duration, the transmission control unit transmits to the engine management unit, a management command whereby the engine is managed so that it supplies a torque equal to the maximum torque value;
the transmission control unit receives the torque demand information supplied by the throttle pedal, the torque demand information is compared by the control unit with a maximum torque value, and when the torque demand becomes higher than the maximum torque value, the transmission control unit transmits to the engine management unit, a management command whereby the engine is managed so that it supplies a torque equal to the maximum torque value, except in the event of a sudden increase in the demand for torque;
in the event of a sudden increase in the demand for torque, during which the torque demand becomes higher than the maximum torque value, the transmission control unit transmits to the engine management unit a management command whereby the engine is managed so as to provide a torque which is higher than the maximum torque value, and if, after a predetermined duration, the torque demand remains higher than the maximum torque value, the transmission control unit transmits to the engine management unit a new management command whereby the engine is managed so that it supplies a torque equal to the maximum torque value;
the maximum torque value corresponds to a maximum permissible torque that can be transmitted through part of the vehicle driveline;
the transmission is connected to the engine by a hydraulic torque converter of the lockup type, and when the converter locks up, the transmission control unit sends to the engine management unit a management command whereby it cannot deliver a torque higher than a maximum lockup torque;
the ratios of the transmission are determined by whether friction couplings are disengaged or engaged, and when a ratio is engaged, the transmission control unit sends to the engine management unit a management command whereby it cannot deliver a torque that is higher than a maximum engagement